Push-out resistance of threaded wooden dowels in cross-laminated timber with hardwood cross-layer

Europe is experiencing a shift in timber resource availability, with a decline in softwoods and an increase in hardwoods, creating a need to explore the utilisation of hardwoods, particularly in construction, where softwoods have traditionally been predominant. This research aimed to assess the potential of using hardwood in hybrid, doweled cross-laminated timber (DCLT) fabricated with pre-dried threaded beech dowels. The objective was to evaluate the push-out resistance of beech dowels in a three-layer DCLT with spruce in the outer longitudinal layers and beech, poplar, or spruce in the cross-layer. The DCLT specimens were conditioned at various temperatures and relative-humidity (RH) levels before the push-out test. The specimens with beech cross-layer exhibited a higher push-out resistance than those made entirely of spruce. In contrast, using poplar in the cross-layer showed no considerable difference in push-out resistance compared to using spruce. Exposure to 70 °C and 10% RH for three days decreased the push-out resistance in all groups due to extreme shrinkage of the lamellae, whereas exposure to 20 °C and 65% RH for either 60 days or 240 days resulted in higher push-out resistance for DCLT with a beech cross-layer.